1. Field of the Invention
The present invention relates to compositions for forming epoxy adhesive compositions containing acrylate rubber and to the compositions thus produced.
2. Description of the Prior Art
Various epoxy resin compositions that do not contain an acrylate rubber as a modifier are known to the prior art. For example, acrylic acid is suggested as a curing agent for epoxy resins in Rev. Gen. Caout. Plast., 1973 50(11), 890-892. More recently, U.S. Pat. No. 4,028,432 to F. Dawans has taught the use of polybutadiene having carboxylic substitution as a modifier for a liquid epoxide resin.
The polymerization of a major amount of an alkyl methacrylate monomer, e.g., 2-ethylhexyl methacrylate, in the presence of a minor amount of an epoxy resin to form adhesive compositions is shown in Japanese Kokai No. 78/57,237.
More recently, U.S. Pat. No. 4,051,195 to W. F. McWhorter suggested blending epoxide resin and a polyacrylate or polymethacrylate ester of a polyol which contained more than one terminal acrylate or methacrylate group. This blend could then be cured using conventional epoxide resin crosslinking agents. The compositions shown in this patent do not contain a monomer soluble initiator capable of reacting with a monoethylenically unsaturated alkyl acrylate or methacrylate to form an acrylate rubber moiety. In the McWhorter compositions, the curing agent first reacts with the epoxide groups to form substituted amine and hydroxy groups. The thus formed amine will then react with the acrylate double bond. The result is the formation of substituted amine groups and saturated carbon to carbon linkages.
More recently, in copending U.S. patent application Ser. No. 316,469, filed Oct. 30, 1981, now abandoned, it has been suggested to modify epoxy resin with a lesser amount of a polyacrylate rubber by forming a reaction mixture comprising epoxy resin, acrylate or methacrylate monomer, and initiator and polymerizing it to form the polyacrylate rubber-modified epoxy resin. In such a system, however, use of more than about 20-25 parts by weight of monomer per hundred parts by weight of epoxy resin was found to undesirably increase the viscosity of the resulting product so as to cause gellation in many cases. Such a result precluded the normally desired flowability at room temperature which was needed for the adhesive composition.